- An international team of astronomers
have measured how fast the Universe is expanding and from that its age.
They have found it to be larger and older than previously thought.
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- The rate at which the Universe is expanding
is measured by a number called the Hubble Constant. It can also be used
to calculate how big and how old the Universe is.
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- The researchers used a method that avoids
the built-in uncertainties in other techniques and calculated the age to
be about 15 billion years old.
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- Astronomers have been arguing over the
Hubble Constant for decades. Measuring it accurately was one of the reasons
why the Hubble Space Telescope was built.
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- American astronomer
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- The Hubble Constant is named after American
astronomer Edwin Hubble, who in the 1920s found that other galaxies were
moving away from ours.
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- "The Universe as a whole is expanding,
like a lump of bread dough rising," said Dr Jim Lovell, leader of
the team that made the measurement. "Like currants in the dough, the
galaxies are all moving away from each other."
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- "The further away a galaxy is, the
faster it is moving away from us. The Hubble Constant links the galaxy's
distance with its speed."
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- To measure the Hubble constant, Dr Lovell
looked at distant objects in space.
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- Distant quasar
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- "We have been looking at light from
a very distant quasar - a galaxy with an extremely bright centre,"
he said.
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- "Quasars usually look like small
spots but this one looks like a ring. Its image has been distorted by the
gravity of a galaxy lying between us and the quasar.
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- We're seeing a sort of mirage of the
distant quasar."
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- The process that makes the mirage is
called gravitational lensing, and was predicted by Einstein.
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- Light that ends up on one side of the
ring has travelled along a different path to the light on the other side,
he said.
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- "These paths are different lengths.
When the quasar puts out more radiation, one side of the ring varies before
the other. We put that time-lag together with other information we know
about the system - redshifts and angles - and out pops the Hubble Constant."
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- Gravity lens
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- The technique sounds simple but it has
taken until now to use it successfully.
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- This "gravity lens" is called
PKS 1830-211 and was discovered in 1991 by astronomers from the Australia
Telescope National Facility (ATNF), the University of Tasmania and Nasa's
Jet Propulsion Laboratory.
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- It is the strongest gravitational lens
ever found - 10 times brighter than any other known lens. It is 14 billion
light-years away, while the galaxy distorting its image is 8 billion light-years
away.
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- "As more good lens systems become
known, more groups are trying to measure the Hubble Constant in this way,"
said Dr Lovell.
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- Our value of the Hubble constant is about
20% lower than the one got with the Hubble Space Telescope in 1994."
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